1. Field of the Invention
The present invention relates to a method for managing a media type supported in a Push-to-talk (PTT) Over Cellular (PoC) session, and a PoC system and a PoC User Equipment (UE) for implementing the same. More particularly, the present invention relates to a method for, when a specific PoC client participating in a PoC session withdraws from the PoC session, processing one or more media types that were negotiated to be usable by the specific PoC client while participating in the PoC session, and a PoC system and a PoC UE for implementing the same.
2. Description of the Related Art
Development of mobile communication technologies and the expansion of communication networks have led to the provision of various services and applications which use mobile telephones. In addition to the basic voice communication service, users are demanding more diversified services, including a positioning service, a multimedia service, and a Push to Talk (PTT) service. In particular, the PTT service supports various supplementary functions such as instant messenger and status display, as well as group and voice communications, which have been provided by conventional radio transmitters or trunked radio systems (TRSs).
Efforts have been made to establish a standard for the PTT over Cellular (PoC) service which employs such a PTT function in a mobile communication network. One feature of the PoC service that is different from the conventional mobile communication service is that it belongs to a plurality of sessions so that the user can communicate while moving between sessions if necessary. The requirement that a user must be able to communicate while moving between a plurality of PoC sessions, that is, the requirement for a multi-session function, are specified by the Open Mobile Alliance (OMA). The OMA is a forum for defining standards for mobile communication services.
The PoC V2.0 system supports a PoC multimedia communication service. To this end, the PoC V2.0 system defines new types of multimedia, such as video, audio and text, in addition to voice. When a PoC session is opened, a media type to be used in the PoC session is determined through negotiations between a PoC server and a PoC client. In addition, it is possible in the current PoC system to display multi-streams, such as video or images, due to advancements made in the capabilities of user equipment.
The multimedia mentioned above is formed with a combination of one or more media types. “Media type” may refer to various types of media, for example, audio such as music, video such a moving picture, an image such as s still picture/photograph, text, and a file, as well as voice specified as speech or PoC speech, and also may refer to a plurality of the same types of media streams.
When a PoC session is opened in the PoC system supporting a plurality of media types as described above, the PoC server opens the PoC session permitting any combination of the media types to be used by PoC clients that participate in the PoC session. In other words, when a PoC session is opened, various media types supportable in the PoC session are obtained through negotiations. In addition, the negotiation of the media types which can be supported in the PoC session is carried out again when another PoC client participates in the PoC session after the PoC session has been opened.
After a PoC session is opened through the negotiation of media types, as described above, one or more media types to be actually used in the PoC session must be supported by at least two PoC clients so that transmission and reception of the one or more media types may be meaningful. However, according to the conventional PoC system, one or more media types to be supported in a PoC session are managed in such a manner as to carry out negotiation of media types only upon opening a PoC session or joining an ongoing PoC session.
If one or more participating PoC clients withdraw from the PoC session, and only one PoC client which uses one or more media types used by the withdrawn one or more PoC clients in the PoC session remains, there will be no PoC client left that is able to receive the corresponding one or more media types.
Consequently, even though a PoC client remains that can transmit media in the corresponding one or more media types, there are no PoC clients that can receive the one or more media types, thereby causing error and waste of resources.